If this is your first visit, be sure to
check out the FAQ by clicking the
link above. You may have to register
before you can post: click the register link above to proceed. To start viewing messages,
select the forum that you want to visit from the selection below.

I wanted to learn about refrigeration

I do not know if I am allowed to post on this thread. Its not a direct reply to the discussion but as you are refrig people perhaps it will be OK. If not please let me know and I will delete it.

I had on old freezer go out and as I wanted to learn about refrigeration I got a non functioning dual stage pump and after replacing a seized bearing I was off to a good start. The capillary tube had a hole in it where it vibrated against the metal chassis.

I put in a new dryer and cut out the piece with the hole and pulled a vacuum which went down to the minimum on the gauge . I heated the oil with a watlow heater and pulled vacuum for several hours for several different days and closed it off and it held for several days. . I was waiting on a wjl 6000 leak tester. When it arrived I began charging and the temp went down to 10 F. I added a bit more and the suction line frosted. I tested for leak with the tester and had a couple spots indicating leak. I decided to back off a lot and hook up a pt100 temp probe to each line. I had at this point 0 suction pressure and about 90 high side.

The temp of the high line was around 105 degrees and the temp of the suction was around 65. At this point.. The evaporator, which it is an old not frost free , was around ¾ frosted at this point. I decided to add r134 until I began to lower the suction line temp I added very little and the suction temp gradually went down to 50 which I thought was good. The inside air temp went back down to 12. Then all of a sudden the suction line frosted so I turned it off to let it settle.

One thing I am concerned about is as the suction line temp was going down from 65 to around 50 the evaporator not only began gurgling but it had a fairly loud knocking which I had never heard this unit do this before when it was working. Also , is 10 F what I should aim for as far as air temp inside the freezer or would a higher temp be ok. the freezer did not cycle out even though I was at 10. Also the wjl-6000 indicates several leaks but the pressure holds from day to day.

The best I can do for you is give you a few tips. You're kind of on the right track. It would help if I knew what kind of machine you're working on but for now it won't matter too much. First, start over and vacuum the machine to 29"hg in a vacuum. Shut the low side gauge off and wait 30 minutes. R134a is heavier than air so it's possible your leak tester is adjusted too high. If the gauge needle doesn't move, look on the model tag for the correct amount of R134a to use. Then use a charging cylinder to add the correct amount of R134a. If you have both low and high side hoses connected to the system you can charge through both hoses. Close off the gauges and watch the pressures. The low side may start out running in a vacuum and slowly climb. Depending on the system 0 lbs might be normal for the low side up to 3-4 lbs. Check the high side pressure against the ambient temperature (use a R134A Temp-Press chart). You can get an idea if everything is ok after a few hours but you need to give it 24 hours for temperatures to stabilize.

We both know I can't teach you refrigeration repair in a few posts. Back in the old days when R12 was used it was possible to charge a system by the frostback method because R12 was very forgiving. Not so with R134a. Here's the temperature pressure chart for R134a.

Thank you for the reply Rick.

The unit is a Woods freezer Very small, the smallest i have seen in an upright. I could not find the charge data. There is extensive schematic , mechanical diagram and serial number on the unit but I don't see the charge data. I did begin by weighing in 5.5 ounces on a laboratory scale.

Although I would like to fix this unit , the primary intention is a learning exercise. As far as using it I was running it for several years on a temp controller at 37 degrees to use it as a fridge in my shop to store varnish and chemicals. Do you think since it is cooling that i might run it for a while and see what it does as long as I don't let the suction line get too cold?

Also the chart you give shows 103 degrees at 90 psi which is nearly the exact amount I had which was 105 on the high side line at 90 psi while the unit as running. i have some refrigeration books but they cover big units mostly and do not get into detail on small units specifically.

its working

after I shut it off when the suction line frosted yesterday , I let out maybe 1 second discharge and let it set until today. I turned it on today . 45 ambient.
Put several gallons of water in it. After 75 minutes it is down to 10.
Temp split is 66/96. Pressure split is -1/80. The crazy knocking is not happening and I hear a nice gurgling. Maybe before with the overcharge there was freezing in the evaporator causing the knocking.

OK, you're giving me too much useless information. I don't even know what a temperature/pressure split is. What's the low side pressure and what's the high side pressure? The gurgling sound is refrigerant boiling in the evaporator. The knocking is most likely an overcharge. Small machines don't use an expansion chamber. You're over thinking the entire process and when it comes to refrigeration it's easy to overthink then second guess. In its simplest form, charge the system with the correct amount R134a, Watch your pressures, is there frost on the evaporator, is the condensor warm, then everything is working correctly. Adjust the pressures if necessary after 2-3 hours run time. I'm guessing around 0 on the low side and 90 on the high side. When the suction line starts to frost back to the compressor, that's called a "frostback". While the machine is still running slowly let out some gas until the frost starts to disappear then close the valve. It's extremely difficult to adjust the pressures that way. It's also illegal to knowingly vent refrigerant into the atmosphere or work on sealed systems without being certified by the EPA. However, I've never seen any refrigeration police, just thought you should know.

its working now

The low side pressure is -1 and the high side if 90.
The unit went down to 8 degrees and shut off.
everything inside is frozen. It took about 2 hours to get to this point. After a while i went back to it and it had cycled back on and was going back down to 8 degrees. Is this the typical range for a freezer with the thermostat set about midway? I have heard that a domestic freezer runs at 0. The temp split I was referring to was the suction line temp and the high side temp as I has attached a thermocouple to these line to measure the temp. I guess that is not typically done. I do not know what you mean by "adjust the pressures'' . From my level of observation it would require either an addition or removal of refrigerant to change the pressure.Is that correct? Thank you for your instruction.

Rick, concerning your EPA comment. I have occasionally taken old fridges to the metal recycling and now they reject them if they are still sealed. I looked up the EPA regs and found this at EPA website:
''Individuals removing refrigerant from small appliances, MVACs, and MVAC-like air conditioners, when preparing them for disposal, are not required to be certified technicians. However, the equipment used to recover refrigerant from appliances prior to their final disposal must meet the same performance standards as refrigerant recovery equipment used for servicing.
EPA no longer requires persons involved in the final disposal of appliances to certify to their EPA Regional Office that they have obtained and are properly using EPA-certified refrigerant recovery equipment.'' https://www.epa.gov/section608/stati...l-requirements. is this accurate information?

Rich, we don't get into deep detail on sealed systems here, there is way too much involved, and learning to do sealed system work takes time and patience, and going out with another tech to do "HANDS ON" work only is the best way to learn.